The present invention relates to a process for manufacturing TFT liquid crystal displays and, more specifically, to a process for manufacturing pixel electrodes with rough diffusers for serving as the reflection members of TFT-LCD devices.
With the advance of techniques for manufacturing thin-film transistors, the liquid crystal displays (LCD) are widely applied in electrical products, such as PDAs, laptops, cellphones, high resolution television sets, etc. due to advantages as smaller size, portability, and lower power consumption. Particularly the up-to-date reflective LCD device is usually performed by utilizing the reflection of light incident from outside, wherein the pixel electrodes made of metal materials are applied to serve as reflection members. Thus the light reflected form the pixel electrode performs desired images on the displays through liquid crystal molecules and color filters. The reflective type liquid crystal display which does not require a backlight has been vigorously developed because this type of display is power saving, thin and lightweight. In addition, since members for the backlight are not necessary, the cost may be reduced.
Notedly, the deeply concerned and important key point is how to promote efficiency of light reflection because the light source of the reflective type LCD comes from the external illumination. In prior art, polarizing plates are introduced to adjust the phases of incident lights for increasing reflection intensity. However, it is not practical to apply the additional polarizing plates into the reflective type LCD. Another solution is to fabricate the pixel electrodes with rough surface for serving as the reflection diffusers for completely utilizing external illuminations, promoting efficiency of reflections and increasing contrasts.
Please refer to FIG. 1, the cross-sectional view of TFT-LCD with rough reflection fabricated by prior art is shown. The related process comprises follow steps. A gate structure 12 is defined on a glass substrate 10 first. Then an insulating layer 14 is deposited on surfaces of the gate structure 12. A semiconductor layer 16 such as amorphous silicon, a doped silicon layer 18 and a metal layer are sequentially formed on the gate structure 12. Next a photolithography procedure is performed to define a drain structure 20 and a source structure 22. After the TFT-LCD 24 is fabricated, an additional step is performed to form plural bumps 26 made of photoresists in the areas for defining pixel electrodes. Next a passivation layer 28 such as polymer material is coating on the bumps 26. And a pixel electrode 30 is formed above those layers. Thus, the reflection efficiency is promoted due to the pixel electrode 30 having a rough and uneven surface.
However, for forming the bumps 26, it is necessary to deposit a photoresist layer on the glass substrate 10 first, and to perform the lithography, developing, and baking steps for defining bump patterns. It is required to fabricate an additional reticle for performing the above procedures. Therefore the cycle time is prolonged and the throughput is reduced cause the additional photomask and related steps. Additionally, the procedures of defining bumps 26 usually damage the glass substrate and devices because the thin-film transistor 24, scan lines, data lines, and capacitors are formed before those steps of defining bumps 26.
The first objective of the present invention is to provide a method for manufacturing a TFT-LCD device having pixel electrodes with rough surfaces for serving as reflection members.
The second objective of the present invention is to provide a method of forming pixel electrodes with rough surfaces, wherein three different types of bumps are mutually stacked arbitrarily to make surfaces of the pixel electrodes rough and uneven.
The third objective of the present invention is to provide a method of defining bumps below pixel electrodes for making the pixel electrodes have rising and falling surfaces without additional lithography etching procedure.
The four objective of the present invention is to provide a process for manufacturing TFT-LCDs with rough reflections, wherein various bumps for making the reflection members have rough surfaces are formed in the steps of defining patterns of the thin-film transistors simultaneously.
A method of forming a TFT-LCD device with a rough pixel electrode for serving as the diffuser member is disclosed hereinafter. The method comprises the following steps. First, a first metal layer is formed on a substrate. And a first etching procedure is done to etch the first metal layer for defining a gate structure. Then a first insulating layer is formed on the gate structure and the substrate. A semiconductor layer is formed on the first insulating layer above the gate structure. Next a second insulating layer is deposited on the semiconductor layer and the first insulating layer. A second etching procedure is done to etch the second insulating layer to define an etching stopper above the gate structure. Subsequently a second metal layer is formed thereon and a third etching procedure is done then to etch the second metal layer to define drain/source structures aside the etching stopper. Next a passivation layer is formed on the drain/source structures and the first insulating layer, wherein the passivation layer is etched to expose a portion of the drain/source structures. A pixel electrode is then formed on the passivation layer wherein the pixel electrode is electrically connected to the drain/source structures.
It is noted that the pixel electrode have the rough surface duplicated from at least one sort of bumps defined above the substrate. The bumps comprise first bumps, second bumps, and third bumps, wherein the first bumps are made of the first metal layer and defined in the first etching procedure simultaneously, the second bumps are made of the second insulating layer and defined in the second etching procedure simultaneously, and the third bumps are made of the second metal layer and defined in the third etching procedure simultaneously.